1. Field of the Invention
The present invention relates to a power supply backup device used for a RAM included in portable electronic apparatus such as an electronic notebook.
2. Description of the Related Art
Portable electronic apparatus such as an electronic notebook or the like generally contains a main battery as a main power supply and an auxiliary battery as an auxiliary power supply. Usually power is supplied from the main battery to a nonvolatile memory for storing data, etc. Then, if the main battery goes wrong or when the power supply capability of the main battery comes down by consumption, the power supply path is switched to the auxiliary battery. In this case, the consumption or abnormality of the main battery is detected by sensing a voltage drop of the main battery below a specified value.
In an electronic appliance arranged as described, when the main battery or the auxiliary battery are replaced with new one if both are dismounted simultaneously by mistake, the power supply to the RAM is discontinued, so that data in the RAM will be lost. To prevent a data loss accident such as this, there is conventionally provided a mechanism which prevents simultaneous dismounting of the main battery and the auxiliary battery. The appliance needs to be provided with a battery change switch, a battery cover, a battery detection pin or the like, and therefore a scheme of preventing loss of data by this kind of mechanism results in an complicated construction of the appliance.